The present invention relates to a semiconductor device on which a high-frequency circuit is mounted and to an electronic apparatus comprising a high-frequency mounting circuit board to which the semiconductor device is connected by soldering.
In recent years, higher-speed operation and increasing miniaturization have been required of electronic apparatuses in an information communication field and in an information processing field. As a representative of these apparatuses, a mobile telephone apparatus can be listed. To increase the operating speed of an apparatus comprising a high-frequency mounting circuit board, such as a mobile telephone apparatus, and reduce the size thereof, it is not only necessary to increase the operating speed of each of the high-frequency mounting circuit board and a semiconductor device in which a high-frequency circuit is mounted and reduce the size thereof but also necessary to improve a structure for mounting such as a package. In particular, the electrode structure of a package which is soldered to the mounting circuit board and the structure for mounting a semiconductor element, such as a package, are important.
FIG. 7 shows a schematic structure of mounting of a semiconductor device 10 on a mounting circuit board 1. The semiconductor device 10 comprises: a semiconductor element 35; a mold resin portion 28 which constitutes a package upper portion; and a package lower portion 11. The package lower portion 11 comprises: a substrate 5; metal patterns 6 and 15 formed on the first and second surfaces 37 of the substrate 5 (the upper and lower surfaces thereof in the drawing), respectively; and an upper electrode 13 and an external terminal 14 having different surface metal plate layers 8 and 17 formed on the respective surfaces thereof. On the surface metal plate layer 8 on the first surface of the substrate 5 for semiconductor device of the package lower portion 11, the semiconductor element 35 fixed by using an adhesive agent 9 is placed and electrically connected to the upper electrode 13 by a conductive wire 12.
On the second surface 38 of the substrate 5 for semiconductor device of the package lower portion 11, the external terminal 14 and a mounting land 3 on the mounting circuit board 1 are electrically connected by a solder connection portion 19. On the mounting circuit board 1 of FIG. 7, a wiring pattern 2 except for the portion thereof corresponding to the mounting land 3 connected to the semiconductor device 10 is covered with a solder resist 4 and insulated thereby. The metal pattern 15 on the second surface 38 of the package lower portion 11, except for the portion thereof corresponding to the external terminal 14, also has a surface thereof covered with a solder resist 18.
Each of the plate layers 8 and 17 is formed of, e.g., a Ni/Au double-layer plate. The purpose for plating the surface with the Ni/Au double-layer plate is to improve the connectivity of wire bonding and soldering.
When the semiconductor device 10 having a structure shown above is connected to the amounting circuit board 1, a height 20 of the solder resist 18 adjacent to the external terminal 14 of the package lower portion 11 from the second surface 38 of the substrate 5 is larger than a height 21 of the surface of the external terminal 14 from the second surface 38 of the substrate 5, as shown in FIG. 7. This is because the thickness of the Ni/Au layer (Ni: 3 to 6 μm, Au: 0.1 to 0.3 μm) as the surface metal plate layer 17 is sufficiently smaller than the thickness of the solder resist 18.
Because of the height difference, the external terminal 14 is away from the mounting land 3 so that the volume of the solder connection portion 19 is increased. When the amount of the solder is small, the amount of the solder filled in the increased volume becomes insufficient so that a solder skip occasionally occurs in the solder connection portion 19 to cause defective mounting. When the amount of the solder is large, the solder forms an extruded solder portion 23 between the solder resists 4 and 18, scatters, or causes a short-circuit (bridge) between the external terminals 14. There is also a case where a ball-shaped extruded solder portion 24 develops from the wiring pattern 2 on the mounting circuit board 1.
When the solder portions 23 and 24 extruded from the mounting land 3 on the mounting circuit board 1 and from the external terminal 14 in FIG. 7 become larger, they cause a short circuit between the different mounting lands 3 on the mounting circuit board 1 or between the external terminals 14, thereby preventing the normal operation of the semiconductor device 10 and the mounting circuit board 1. Even when the extruded portions are small, they cause a problem of degraded high-frequency characteristics such as an increased loss in electric signal in a high-frequency range exceeding 500 MHz or a higher level of noise which is mixed in an electric signal as a result of crosstalk to cause incorrect reading of the electric signal, though no problem is encountered in a low-frequency range of 100 MHz or less or in dc operation.
When the principal portions of the first and second surfaces 37 and 38 of the substrate 5 for semiconductor device are formed of the metal plate layers each having a uniform thickness as shown in FIG. 7, a stress resulting from a temperature increase during solder mounting is likely to be placed thereon. When the semiconductor element is fastened to the metal plate layer or the like by using an adhesive agent or the like, delamination occasionally occurs at the interface between the mold resin covering the semiconductor element and the metal plate layer due to the stress resulting from the temperature increase during solder mounting. When such delamination or the like occurs, moisture or the like is likely to reach the semiconductor element as a result of time-varying changes so that the reliability of the semiconductor device 10 is significantly degraded.
FIGS. 8A and 8B show an example obtained by modifying the structure of electrodes on the mounting circuit board shown in a prior patent document (Japanese Laid-Open Patent Publication No. 2005-32931). FIG. 8A schematically shows a circuit component 46 mounted on a conventional mounting circuit board 50. In the mounting circuit board 50, a circuit wiring portion 42 and a conductor 44 made of a land 43 are fastened onto an insulating substrate 41. An insulating resin 45 is formed on the insulating substrate 41 to cover the conductor 44 for preventing the solder from flowing out and providing insulation between the conductors 44. The insulating resin 45 on the land 43 has an opening formed therein. The land 43 is partially exposed through the opening and connected to the circuit component 46 by a solder connection portion 47.
In the mounting circuit board 50, however, the upper surface of the land 43 is depressed to a lower level by the thickness of the insulating resin 45. When the circuit component 46 is mounted by soldering on the land 43 of the mounting circuit board 50, the quality of the state of the solder connection portion 47 is determined by the amount of the solder. That is, when the solder is coated in a large amount in excess of the layer thickness of the insulating resin 45, the excessive solder causes the formation of a solder ball which does not contribute to connection or the flowing out of the solder so that a short circuit occurs between the adjacent conductors 44. Conversely, when the solder is coated in a small amount, a solder skip or the like occurs in the solder connection portion 47 to cause the problem of faulty connection between the electrode portion of the circuit component 46 and the land 43.
To solve the problem, a mounting circuit board 55 having a structure in which the land 43 connected to the circuit component 46 is protruding higher and thicker than the insulating resin 45 is used, as shown in FIG. 8B. The protruding portion 48 ensures reliable connection to the circuit component 46 and allows the remaining excess portion of the solder to escape between the protruding portion and the insulating resin. The arrangement allows the setting of the amount of the solder such that it is slightly larger than required to connect the protruding portion of the land 43 and the solder connection portion of the circuit component 46 within a given range. As a result, the state of the solder connection is surely improved compared with the state shown in FIG. 8A. It is to be noted that the prior patent document shows the case where a 2-terminal circuit component is mounted. In the case of mounting a semiconductor element typically having the 2-digit number of electrode terminals or more and having a high-frequency circuit integrated therein, an extra modification should be made.
In FIG. 8B, a solder ball or an extruded solder portion may be formed between the protruding portions 48 or on the outer side of the insulating resin 45 on which the mounted circuit component 46 is mounted. When such a solder ball or an extruded solder portion is formed on the mounting circuit board to which a high-frequency signal is transmitted, the high-frequency characteristics may be degraded, as mentioned above in the description of FIG. 7.
In summary, it can be said that, to solve the problems shown above, the prior patent document has modified the structure of the electrode such that the height of the electrode is larger than the height of the solder resist, thereby suppressing a short circuit between the adjacent electrodes and faulty bonding between the conductor and the terminal of the component or the like (see, e.g., Japanese Laid-Open Patent Publication No. 2005-32931). Otherwise, the region to which the remaining excess portion of the solder in the solder bonding portion is allowed to escape is formed in the board so that a short circuit or faulty bonding is suppressed (see, e.g., Japanese Laid-Open Utility Model Publication No. 04-87673 and Japanese Laid-Open Patent Publication No. 05-327196)